Conventionally, it is possible to measure the current consumption of an electronic device by measuring the voltage on the terminals of a resistor connected, for example, between a voltage source and the processing unit. These resistors are generally connected to an operational amplifier which delivers as output the voltage on the terminals of the resistor.
However, some applications require the use of active loads, for example processing units, consuming a current of which the value may vary very substantially during a very short time. For example, it is possible for a processing unit to consume a current having a mean value of 0.3 microamperes for several seconds, then, due to the implementation of a specific operation, to consume a current of 3 milliamperes for 0.5 milliseconds.
It is thus necessary to be able to measure a current having a broad dynamic range, at a high frequency in order not to miss the measurement of very brief events, such as current consumption peaks.
It is not currently possible to perform such measurements with a single resistor connected to an amplifier. In fact, amplifiers capable of operating at high frequencies generate noise that is too high to be suitable for measuring very low current.
Measurement circuits also exist which include two resistors, each connected to an amplifier, one dedicated to measuring low currents, the other to measuring high currents, and a switching system allowing the voltage on one or the other of the two resistors to be read; however, the transition does not take place quickly enough and it is possible that some samples are lost during the switching.